This invention relates to solenoid operated valves and, more particularly, to such a valve wherein the solenoid surrounds the flow line and which is adapted for pulsed operation.
Automotive air conditioning systems in the past typically utilized either a thermostatic expansion valve or an orifice to control the flow of refrigerant to the evaporator. While such systems operated generally satisfactorily, the amount of control thereover was minimal. Since automotive control systems have become increasingly more sophisticated, with onboard microcomputers being provided for controlling such functions as engine speed, fuel flow, fuel mixture, transmission ratio, etc., it has been proposed to utilize an electrically operated expansion valve under control of the onboard microcomputer in the air conditioning system. Such valves are typically controlled in a pulse width modulated manner, which requires that the valves be pressure balanced to avoid placing an undue load on the automotive electrical system, which would occur if the valve operator had to open the valve under a differential pressure of at least 300 psi, which is typical in an automotive air conditioning application. Satisfactory results have been achieved in the past with a valve design wherein the solenoid extends outward at a right angle from the refrigerant fluid flow line with the motion of the solenoid plunger, which typically includes the valve member, being at right angles to the fluid flow. While such a valve operates in a satisfactory manner, under certain applications it is desirable to have what is referred to as an inline valve, where the control solenoid surrounds the flow line. Such a valve is advantageous because it results in a smaller overall package and its operation is quieter than a right angle valve. It is therefore an object of this invention to provide such a valve.
Prior constructions of inline solenoid operated valves have utilized a conical plunger which contacts a valve seat. A problem encountered with this type of arrangement is that mechanical wear due to the impact of the plunger against the seat degrades the valve performance. With the pulse width modulation control systems which are utilized in automotive air conditioning systems, a valve must last, on the average, for sixty million cycles. The impact of the plunger against the valve seat, and the resulting wear, is generally the limiting factor in valve life. It is therefore a further object of this invention to provide an inline solenoid operated valve wherein physical contact and impact between the flow control surfaces is eliminated.